Multilayer heat sealant structures, packages and methods of making the same

ABSTRACT

The embodiments of the present invention relate to multilayer thermoplastic structures having improved sealability and tearability. More specifically, the present invention relates to a multilayer heat sealant structure having at least three layers that may be coextrusion coated or otherwise laminated to a substrate, such as metallized polymeric material, foil, or other substrates.

This Application is a divisional of prior application Ser. No.11/871,459 filed Oct. 12, 2007, now allowed, which is acontinuation-in-part of prior application Ser. No. 10/664,491, filed onSep. 17, 2003, abandoned, which applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

Coextruded multilayer structures having improved sealability areprovided. More specifically, the coextruded multilayer structurescomprise at least three layers wherein a first layer comprises a firstthermoplastic polymeric material, a second layer comprises low densitypolyethylene coextruded with and disposed adjacent to the first layer,and a third layer comprises a single site catalyzed polyethylene,wherein said third layer is coextruded with the first and second layersand further is disposed adjacent to the second layer. The coextrudedheat sealant structures may be laminated to one or more substrates.Moreover, the coextruded heat sealant structures may be heat sealed toanother coextruded heat sealant structure to form packages forming aspace for a product therein. The structures of the present invention maybe particularly useful for flowable products, such as, for example,condiments including, but not limited to, catsup, mustard, mayonnaiseand the like.

BACKGROUND

It is generally known to provide multilayer structures that may beutilized as heat sealant structures to form packages for products, suchas, for example, flowable products. Many multilayer structures are knownhaving a variety of properties, such as heat sealability, flowability,and the like.

Packages for enclosing products are typically made by forming athermoplastic polymeric structure into a shape to accommodate theproduct, placing another thermoplastic polymeric structure over theproduct and then heat sealing the structures together to maintain theproduct within the two structures. Packages for products may also bemade by forming a thermoplastic polymeric structure into a pouch, orotherwise folding a thermoplastic polymeric structure over itself,filling the structure with a product, and then heat sealing thestructure closed. The packages made from the above, however, can haveproblems in their heat-sealing and tearability properties. These issuesare especially problematic if the package, containing a flowableproduct, is intended to be opened by a consumer wherein a combination ofgood seal and good tear properties are desired and necessary.

Certain products, such as, for example, condiments, requirethermoplastic multilayer structures to form relatively small packages.For example, it is well known that catsup, mustard and other likecondiments are packaged in individual serving sizes, especially atfast-food restaurants or the like.

Typical packages for flowable products, such as condiments, have wallsmade from multilayer thermoplastic structures that are not typicallyeasily torn, such that the product may not be easily retrieved orotherwise utilized from the package. Therefore, packages may bedifficult to open by young children, the aged or infirm, and other likeindividuals having reduced ability to cause the structures to tear. Thewalls of a package for flowable products, such as, for example,condiments or the like, should be easily tearable without also causingthe product to be spilled or otherwise lost.

Moreover, typical packages for flowable products, such as, for example,condiments and/or wrinkles or the like, do not provide good seals whenheat sealed because of contaminants and/or wrinkles that may be presentwithin the heat seal zone. Typically, condiment packaging is made by aknown process called vertical form, fill and seal (VFFS), whichcomprises bringing together two thermoplastic polymeric structures inface-to-face contact and wrapping the structures around product fillingtubes. The structures are heat sealed on opposite sides of the productfilling tubes in the machine direction to form side seals of thecondiment packages. A heat seal is then placed across the structures inthe transverse direction of the thermoplastic structures below theproduct filling tubes to form a pouch. Product is then delivered intothe individual pouches and the delivery tubes are then extracted fromthe pouches. A final heat seal is disposed to seal the tops of theindividual pouches. Heat seals, however, typically require heat sealzones free of contaminants and/or wrinkles to prevent weak heat sealsfrom forming. Weak heat seals can cause a loss of a flowable productsince a flowable product contained in packages having weak heat sealsmay spill from the packages if the heat seals break or otherwisedelaminate. Moreover, packages having weak heat seals may lose theiroxygen or moisture barrier characteristics.

Typically, to increase the sealability of packages for flowableproducts, a high melt flow thermoplastic material is used as the heatsealant layer. However, high melt flow materials tend to increase thetear resistance of the packages, thereby making it more difficult toopen by using tearing forces.

A need, therefore, exists for a multilayer heat sealant structure havingimproved tearability, while also being easily heat sealed, even in thepresence of contaminants and/or wrinkles. Moreover, a need exists forpackages made from the multilayer heat sealant structure to containflowable products therein, such as, for example, condiments and thelike. In addition, a need exists for structures, packages and methods ofmaking the same that solve the problems associated with prior artstructures and packages for flowable products, such as, for example,condiments or the like.

SUMMARY OF THE INVENTION

The embodiments of the present invention relate to multilayerthermoplastic structures having improved sealability and tearability.More specifically, the present invention relates to a multilayer heatsealant structure having at least three layers that may be coextrusioncoated or otherwise laminated to a substrate, such as metallizedpolymeric material, foil, or other substrates.

To this end, in an embodiment of the present invention, A multilayerstructure is provided comprising a coextruded multilayer heat sealantstructure comprising a first layer comprising a thermoplastic polymericmaterial, a second layer comprising low density polyethylene disposedadjacent to and coextruded with the first layer, and a third layercomprising a single site catalyzed polyethylene for use as a heatsealant layer wherein the third layer is disposed adjacent to the secondlayer and further wherein the third layer is coextruded with the firstand second layers. The coextruded multilayer heat sealant structure maybe laminated to one or more substrates. One of the plurality ofsubstrates may comprise a metallized layer wherein the first layer ofthe coextruded multilayer heat sealant structure is adhered to themetallized layer. The coextruded multilayer heat sealant structure maybe laminated to another coextruded multilayer heat sealant structure.

Moreover, the first layer of the multilayer structure may compriseethylene acrylic acid copolymer, the second layer may comprise a blendof low density polyethylene and high density polyethylene, and the thirdlayer may comprise metallocene-based single site catalyzed polyethylene.Specifically, the third layer may comprise a blend of the single sitecatalyzed polyethylene and low density polyethylene.

In addition, the coextruded multilayer heat sealant structure may becoextrusion coated to the substrate. Moreover, the coextruded multilayerheat sealant structure may be made by blown coextrusion.

The single site catalyzed polyethylene may preferably have a density ofabout 0.912 g/cc and a melt index of about 12 g/10 min at 190° C.Alternatively, the single site catalyzed polyethylene may have a densityof about 0.910 g/cc and a melt index of about 15 g/10 min. at 190° C.

In an alternate embodiment of the present invention, a package for aproduct comprises a first multilayer structure comprising a coextrudedmultilayer heat sealant structure comprising a first layer comprising athermoplastic polymeric material, a second layer comprising low densitypolyethylene disposed adjacent to and coextruded with the first layer,and a third layer comprising a single site catalyzed polyethylene foruse as a heat sealant layer. The third layer is disposed adjacent to thesecond layer and is coextruded with the first and second layers. Asecond multilayer structure is heat sealed to the first multilayerstructure to form the package with a space therein for the product. Thecoextruded multilayer heat sealant structure may be laminated to asubstrate. The substrate may comprise a metallized layer wherein thefirst layer is laminated to the metallized layer.

Moreover, the first layer of the coextruded multilayer heat sealantstructure of the package of the present invention may comprise ethyleneacrylic acid copolymer, the second layer may comprise a blend of lowdensity polyethylene and high density polyethylene, and the third layermay comprise metallocene-based single site catalyzed polyethylene. Morespecifically, the third layer may comprise a blend of the single sitecatalyzed polyethylene and low density polyethylene.

In addition, the coextruded multilayer heat sealant structure of thepackage may be coextrusion coated to the substrate. Moreover, thecoextruded multilayer heat sealant structure may be made by blowncoextrusion. Further, the second multilayer structure may be identicalto the first multilayer structure.

Still further, the single site catalyzed polyethylene of the third layerof the heat sealant structure of the package of the present embodimentmay have a density of about 0.912 g/cc and a melt index of about 12 g/10min. at 190° C. Alternatively, the single site catalyzed polyethylenemay have a density of about 0.910 g/cc and a melt index of about 15 g/10min. at 190° C.

In another alternate embodiment of the present invention, a method ofmaking a multilayer structure is provided comprising the steps ofcoextruding a multilayer heat sealant structure comprising a first layercomprising a thermoplastic polymeric material, a second layer comprisinglow density polyethylene wherein the second layer is disposed adjacentto the first layer, and a third layer comprising a single site catalyzedpolyethylene wherein the third layer is disposed adjacent to the secondlayer, and laminating said first layer of said multilayer sealantstructure to a substrate.

Preferably, the substrate comprises a metallized layer, the first layercomprises ethylene acrylic acid copolymer, the second layer comprises ablend of the low density polyethylene and a high density polyethylene,and the third layer comprises a blend of the single site catalyzedpolyethylene and low density polyethylene.

In addition, the multilayer heat sealant structure made by the method ofthe present invention may be made via blown coextrusion. Moreover, themultilayer heat sealant structure made by the method of the presentinvention may be coextrusion coated to the substrate. Further, thesingle site catalyzed polyethylene may have a density of about 0.912g/cc and a melt index of about 12 g/10 min. at 190° C. Alternatively,the single site catalyzed polyethylene may have a density of about 0.910g/cc and a melt index of about 15 g/10 min. at 190° C.

It is, therefore, an advantage of the present to provide a heat sealablethermoplastic structure that is easily torn and further is easily heatsealed through contaminants and/or wrinkles. Moreover, it is anadvantage of the present invention to provide a heat sealablethermoplastic structure that is laminated to one or more substrates toprovide abuse protections, printability, oxygen and moisture barrierproperties, and other like characteristics. Additional features andadvantages of the present invention are described in, and will beapparent from, the detailed description of the presently preferredembodiments and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of a multilayer heat sealantstructure of the present invention in an embodiment of the presentinvention.

FIG. 2 illustrates a cross-section of a multilayer structure of a heatsealant structure adhered to a plurality of substrates in an alternateembodiment of the present invention.

FIG. 3 illustrates an exemplary package with polymeric structures placedin a face-to-face relationship.

DETAILED DESCRIPTION OF THE INVENTION

Coextruded multilayer structures, packages made therefrom, and methodsof making the same are provided. More specifically, the coextrudedmultilayer structures comprise heat sealant structures comprising atleast three layers wherein a first layer comprises a first thermoplasticpolymeric material, a second layer comprises low density polyethylenecoextruded with and disposed adjacent to the first layer, and a thirdlayer comprises a single site catalyzed polyethylene, which iscoextruded with the first and second layers and further is disposedadjacent to the second layer. The coextruded heat sealant structures ofthe present invention may be laminated to substrates. Moreover, thecoextruded heat sealant structures may be heat sealed to otherstructures to form packages forming spaces therein for products. Thestructures of the present invention may be particularly useful forflowable products, such as, for example, condiments including, but notlimited to, catsup, mustard, mayonnaise and the like.

Referring now to the figures, wherein like numerals refer to like parts,FIG. 1 illustrates a cross-sectional view of a multilayer heat sealantstructure 1 of the present invention. The multilayer heat sealantstructure 1 may comprise a first layer 10, a second layer 12 and a thirdlayer 14. The first layer 10 may comprise a thermoplastic polymericmaterial, preferably useful for laminating to substrates, as shown belowwith reference to FIG. 2. Preferably, the first layer 10 may comprise athermoplastic polymeric material selected from the group consisting ofethylene acrylic acid copolymer, ethylene methyl acrylate copolymer,ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer,ethylene methyl acrylic acid copolymer, and blends thereof. Mostpreferably, the first layer 10 is selected from a thermoplasticpolymeric material that bonds well to foil or other metallized layers.

The second layer 12 of the multilayer heat sealant structure 1 maycomprise a thermoplastic polymeric material that provides increasedstiffness to the multilayer heat sealant structure 1 of the presentinvention. Moreover, the second layer 12 may comprise a thermoplasticpolymeric material that has a relatively high melting temperature,relative to the heat sealant layer 14, described below. Thethermoplastic polymeric material of the second layer 12 thereby enhancesthe burst strength of packages made from the multilayer heat sealantstructure 1 and improves wrinkles that may form during the making of themultilayer heat sealant structure 1. Moreover, the thermoplasticpolymeric material of the second layer may have a relatively low meltindex, especially relative to the material utilized in the heat sealantlayer, as described below. Low melt index materials are useful toprevent sealant squeeze-out during heat sealing, or caulking, of theheat sealant layer. Preferably, the thermoplastic polymeric materialforming the second layer 12 may be low density polyethylene or a blendof low density polyethylene and high density polyethylene.

The third heat sealant layer 14 allows the multilayer heat sealantstructure 1 to be heat-sealed to itself or to other similar filmstructures. Typically, polymeric structures are placed in face-to-facerelationship with each other, and a heat-sealing bar fuses the twopolymeric structures together to form a package 112. FIG. 3 illustratesthe face-to-face relationship of polymeric structures. The arrangementof a first multilayer heat sealant structure comprising a low melt indexlayer 12 (second layer) adjacent to a high melt index layer 14 (thirdlayer) abutting a second multilayer heat sealant structure comprising alow melt index layer 12 adjacent to a high melt index layer 14 providesa unique and superior combination of materials within a sealant surface.

In one aspect, the high melt index layer 14 of the first multilayer heatsealant structure abut the high melt index layer 14 of the secondmultilayer heat sealant structure. In another aspect, at least a portionof the first multilayer heat sealant structure is heat sealed to atleast a portion of the second multilayer heat sealant structure creatinga sealed area 114. In another aspect, the portion is an edge. In anotheraspect, at least three edges are heat sealed to form a package such as abag. Such bags are typically rectangular in shape.

The third heat sealant layer 14 may be made from polyethylene having arelatively low melt temperature and a relatively high melt index, suchas, for example, above about 10 g/10 min, thereby enabling the heatsealant structure 1 to easily flow when melted and fuse when frozen. Byutilizing a material having a relatively high melt index, heat seals maybe created that are relatively strong, especially if productcontaminates the heat seal area on the first structure or if wrinklesare present in the heat seal area. Preferably, the third heat sealantlayer 14 comprises a thermoplastic polymeric material that provides highflow rates, good hot tack, lower seal activation and can easily seal, orcaulk, through any product, irregularities, or wrinkles that maycontaminate the seal area of multilayer sealant structure 1. Single sitecatalyzed polyethylenes are ideal polymeric thermoplastic materials toprovide high melt indexes with relatively low melt temperatures.

Preferably, the heat sealant materials utilized in the third heatsealant layer 14 are single site catalyzed polyethylenes or blends ofsingle site catalyzed polyethylenes with low density polyethylene. Morepreferably, the single site catalyzed polyethylene utilized in the thirdheat sealant layer 14 is Exxon single site catalyzed polyethylene havinga density of about 0.912 g/cc and a melt index of about 12 g/10 min. at190° C., measured by ASTM D-1238. Most preferably, the single sitecatalyzed polyethylene utilized in the third heat sealant layer 14 isDOW INSITE™. single site catalyzed polyethylene technology, having adensity of about 0.910 g/cc and a melt index of about 15 g/10 min. at190° C., measured by ASTM D-1238.

Although the third heat sealant layer comprises a thermoplasticpolymeric material having a very high melt index, this material may becoextruded via blown film coextrusion without difficulty because it isdisposed adjacent to the low melt index thermoplastic polymeric materialof the second layer. The high melt index thermoplastic polymericmaterial may, therefore, maintain its stability during the blown filmcoextrusion process. Without the low melt index thermoplastic polymericmaterial of the second layer 12, the high melt index material of thethird heat sealant layer would not adequately coextrude via blown filmcoextrusion. The unique combination of a thin high melt index polymeradjacent to a low melt index layer allows a much higher melt index to beused than typical for blown films providing sealing, or caulking,characteristics.

Alternatively, the three layers of the multilayer heat sealant structure1 may be made in a two-step coextrusion whereby a first multilayerstructure comprising the first layer 10 and the second layer 12 islaminated to a second multilayer structure comprising the second layer12 and the third heat sealant layer 14. When joined together in thisprocess, the multilayer heat sealant structure 1 is created having thefirst layer 10, the second layer 12 and the third layer 14.

FIG. 2 illustrates a multilayer structure 100 comprising the heatsealant structure 1, described above with reference to FIG. 1, laminatedto a substrate 102. The substrate 102 may be any material useful to adddesired properties to the multilayer structure when utilized in apackage. For example, the substrate may provide barrier protection.Further, the substrates are easily tearable without affecting thesealability of the heat sealant structure 1. For example, the substrate102 may comprise a foil layer 104 or other metallized layers that islaminated directly adjacent to the first layer 10 comprising thethermoplastic polymeric material described above, such as, for example,ethylene acrylic acid copolymer.

Laminated to the foil layer 104 may be further thermoplastic layers 106,108 which may be utilized to provide structure or color to themultilayer structure 100. For example, the thermoplastic layers 106, 108may comprise low density polyethylene. One or both of the layers 106,108 may comprise a colorant thereby providing the multilayer structure100 with color. In addition, an outer abuse layer 110 may be providedcomprising a thermoplastic polymeric material useful for protecting themultilayer structure 100, such as, for example, polyethyleneterephthalate (PET), or other like thermoplastic polymeric material.Moreover, any of these layers may be printed prior to adding to themultilayer structure 100.

The following are non-limiting examples of the present invention:

EXAMPLE 1 Percentage of Melt Index Structure Layer Material SealantStructure (g/10 min) First 100% EAA 13.9% 10.5 Second  70% LDPE 55.6%9.29  30% HDPE Third Heat Sealant 100% mLLDPE 30.5% 15.0

EXAMPLE 2 Percentage of Melt Index Structure Layer Material SealantStructure (g/10 min) First 100% EAA 16.7% 10.5 Second  70% LDPE 46.7%9.29  30% HDPE Third Heat Sealant 100% mLLDPE 36.7% 15.0

EXAMPLE 3 Percentage of Melt Index Structure Layer Material SealantStructure (g/10 min) First 100% EAA 16.7% 10.5 Second 100% LDPE 46.7% 7.0 Third Heat Sealant 100% mLLDPE 36.7% 15.0

Each of these examples shows three layer heat sealant structures. Eachof these heat sealant structures were extrusion coated onto aluminumfoil, resulting in multilayer structures comprising OPP orPET//Polyolefin//foil//first layer 10/second layer 12/third heat sealantlayer 14.

It should be noted that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages. It is, therefore, intendedthat such changes and modifications be covered by the appended claims.

The invention claimed is:
 1. A package for a product comprising: a firstmultilayer heat sealant structure and a second multilayer heat sealantstructure, wherein each of the first and second multilayer heat sealantstructures comprise a coextruded multilayer heat sealant structurecomprising a low melt index layer comprising low density polyethyleneand a high melt index layer comprising a single site catalyzedpolyethylene wherein said single site catalyzed polyethylene has a meltindex above about 10 g/10 min for use as a heat sealant layer whereinthe high melt index layer is disposed adjacent to the low melt indexlayer, and further wherein the high melt index layer is coextruded withthe low melt index layer and further wherein said low densitypolyethylene of the low melt index layer has a melt index lower than amelt index of the single site catalyzed polyethylene of the high meltindex layer; and wherein at least a portion of the first multilayer heatsealant structure is sealed to at least a portion of the secondmultilayer heat sealant structure such that the high melt index layersof the first and second multilayer heat sealant structures abut eachother.
 2. The package of claim 1 wherein each of the first and secondmultilayer heat sealant structures comprise at least one edge, andwherein the at least one edges of the first and second multilayer heatsealant structures are heat sealed.
 3. The package of claim 1 whereinthe low melt index layer comprises a blend of low density polyethyleneand high density polyethylene.
 4. The package of claim 1 wherein thehigh melt index layer comprises metallocene-based single site catalyzedpolyethylene.
 5. The package of claim 1 wherein the high melt indexlayer comprises a blend of the single site catalyzed polyethylene andlow density polyethylene.
 6. The package of claim 1 wherein the packageis rectangular shaped.
 7. The package of claim 1 wherein the package isheat sealed on at least three sides.
 8. The package of claim 1 whereinthe single site catalyzed polyethylene has a density of about 0.912 g/ccand a melt index of about 12 g/10 min at 190° C.
 9. The package of claim1 wherein the single site catalyzed polyethylene has a density of about0.910 g/cc and a melt index of about 15 g/10 min. at 190° C.
 10. Thepackage of claim 1 wherein the at least a portion of the firstmultilayer heat sealant structure is heat sealed to the at least aportion of the second multilayer heat sealant structure.
 11. The packageof claim 1, wherein each of the first and second multilayer heat sealantstructures further comprise a first layer comprising a thermoplasticpolymeric material, wherein said low melt index layer is disposedadjacent to and coextruded with the first layer.
 12. The package ofclaim 11 wherein said thermoplastic polymeric material of the firstlayer comprises ethylene acrylic acid copolymer.